During operation, rotor blades of gas turbines are subjected to high temperatures and high mechanical loads. For such components, use is therefore preferably made of high-temperature nickel-based superalloys that can be strengthened by precipitation of a γ′ phase. Nonetheless, over time the rotor blades can develop cracks that widen further over time. Such cracks can for example arise due to the extreme mechanical loading during operation of a gas turbine, but they can also arise during the production process. Since the production of turbine blades and other workpieces from such superalloys is time-consuming and cost-intensive, there is a need to minimize rejects during production and to ensure a long service life of the manufactured products.
In operation, gas turbine blades are serviced regularly and where necessary replaced, if due to operational loading correct operation can no longer be readily guaranteed. In order to permit further use of replaced turbine blades, these are reconditioned as far as possible. They can then once again be used in a gas turbine. Within the context of this type of reconditioning, it may for example be necessary to carry out deposition welding of a deposition structure onto the damaged workpiece in the damaged regions, in order to reproduce the original wall thickness or shape of the workpiece. This can possibly take place after removal of the damaged location, for example by milling.
In addition, turbine blades that have developed cracks in the production process can in this manner be made suitable for use by means of deposition welding, such that it is possible to minimize rejects during production.
However, many high-temperature superalloys can be welded only with difficulty using conventional welding methods. The resulting deposition structures often have unsatisfactory material properties, which can be traced back to the formation of a columnar solidification front during solidification of the material melted in the course of deposition welding.
There is therefore a need for a welding method that is suitable in particular for high-temperature superalloys such as γ′-hardened nickel-based superalloys and has the abovementioned drawbacks to a reduced extent, if at all.